The present invention is generally directed to apparatus and a method for controlling power delivery to an ultrasonic phacoemulsification handpiece as well as controlling fluid flow to and from an eye during ocular surgery with the phacoemulsification handpiece. More particularly, the invention is directed to apparatus and a method for controlling phaco power delivery and/or fluid flow based upon the amount of thermal energy delivered to an eye over a specific period of time.
Phacoemulsification of cataracts lenses is a medically recognized technique. The method generally includes making of a corneal incision and the insertion of a hand held surgical implement, i.e., handpiece, which includes a needle which is ultrasonically driven in order to emulsify the eye lens. Simultaneously, with this emulsified lens and a vacuum provided for aspiration of the emulsified lens and inserted fluids.
In order to maintain normal pressure within the eye, a balanced salt solution is provided as an irrigation fluid and typically supplied from an elevated chamber. Importantly, the irrigation and aspiration of fluid through the eye must be carefully monitored in order to maintain normal pressure within the eye during surgical procedures. For example, an underpressure condition may cause distortion of the eye which often may interfere with surgical procedures. On the other hand, overpressure may cause damage to the eye.
As hereinabove noted, pressure in the eye may be controlled by physical elevation of the source of irrigation fluid interconnected to the phacoemulsification handpiece. Aspiration of fluid is typically controlled through the use of peristaltic pump or the like.
It should be appreciated that the control of irrigation and aspiration fluids is a dynamic problem. For example, during surgical procedures, fragments of broken tissue may temporarily block an aspiration line or the handpiece. This may lead to a differential pressure which is typically accommodated by stopping or slowing aspiration flow through the regulation of the peristaltic pump connected to the aspiration line.
During aspiration of the lens and aspiration fluid, particles may restrict the aspiration flow from the eye through an aspiration port in the tip of the phacoemulsification handpiece. In order to clear this occlusion, vacuum levels may be increased to create a greater differential pressure across the occluding particle in an effort to move the particle downstream and away from the eye. Typically, particles require much higher force to start movement than it takes to continue movement of the particle to the peristaltic pump. Once a particle moves, it creates a subsequent volume of fluid to take up the space it once occupied. This volume may be momentarily larger than the volume of fluid in the eye, therefore, producing a momentary-dimpling of the eye.
It has been shown that the pressure sensing of this condition is well within the operation of the phaco machine.
However, of further consideration regarding the utilization of phacoemulsification handpiece, is the amount of power delivered to the lens by the handpiece in order to fragment the lens. If too much power is delivered to the handpiece, without concomitant fluid or cooling irrigation fluid, local temperatures of the eye may rise to a level causing localized trauma. On the hand, the entire eye may be heated during the procedure within the anterior chamber which may cause damage. Thus, it is important to not only control the power delivery of a phacoemulsification handpiece, but to provide a means for calculating elevated anterior chamber temperatures in order to prevent any tissue damage due to excess delivered power. Such damage can occur within one to two seconds under adverse heating conditions.
It should be appreciated that in combination with the occlusion of the phacoemulsification needle, as hereinabove described, the fluid flowing from the eye can vary considerably. Thus, heat is not removed from the eye in a generally continuous basis, but, of course, is dependent upon the actual fluid flow as a function of time. Heretofore, consoles for providing irrigation fluid and power of an ultrasonic phacoemulsification handpiece and aspirating fluid from the eye during ocular surgery, have not taken into account energy and power considerations nor utilized same for controlling the operation of the phacoemulsification handpiece.
In addition, prior art devices have not provided any warning to surgeon as to impending damage, i.e., burning, to an eye which can be caused by overheating.
The present apparatus and method provide for such operation.
Control apparatus, by itself, or for use in a control console for providing irrigation fluid and controlling power to an ultrasonic phacoemulsification, or cataract extraction, handpiece and aspiration from an eye during ocular surgery, generally includes a means for monitoring energy provided to the handpiece and means for monitoring energy removed from the eye by aspirated fluid. In connection therewith, a computer responsive to input from the means for monitoring power provided and removed, provides a means for calculating an energy balance over a time interval and determining a matrix of power levels and duty cycle combination that will not generate sufficient heat to create a burn of eye tissue. The power may then be regulated in accordance with the matrix.
In addition, regulation of the fluid flow may also be performed in response to the matrix calculation.
More particularly, the means for monitoring power removed from the eye may include a means for measuring the flow rate of the aspirated fluid and/or irrigation fluid and may further include a means for measuring a temperature difference between the irrigation fluid and the aspirated fluid.
Additionally, output means, which is responsive to the computer means, may provide an indication of eye temperature based upon the energy balance. Specifically, the output means may provide an alarm at a selected eye temperature level. This enables a continuous monitoring of the eye temperature and, in addition, either visual or audible alarm, may be provided at any selected level in order to attract attention to an energy imbalance in order to prevent thermal damage to eye tissue.
Correspondingly, a method for regulating fluid flow and power to an ultrasonic phacoemulsification, or cataract extraction, handpiece, includes the steps of monitoring power provided to the handpiece, monitoring power removed from the eye by the aspirated fluid and calculating, in response to input from the steps of monitoring the power provided and the power removed, a matrix of power levels and duty cycle combinations that will not generate sufficient heat to create a burn in eye tissue. The matrix can then be used to prevent operation of the handpiece outside the matrix or alert a surgeon of potential burns if the handpiece is operated outside the matrix.
Alternately, a test handpiece can be used to determine the matrix and subsequently used handpiece can be prevented from operation outside the matrix or a warning can be given to a surgeon when a handpiece is used outside the matrix.